Fortunately "reasonable" doesn't have to come into play here. PCI auditing standards exist so the human fallacies (potentially) of reason and common sense are mitigated by explicitly defined controls that anyone who deals with credit cards at all must adhere to. Someone like Microsoft, thankfully, would probably be even more scrutinized by auditors, not only because they are Microsoft, but because Microsoft would want to make sure they are compliant.
That being said, PCI, in part, states that credit card info must never be stored, cached, saved...etc., in any device that is directly accessible to the customer or attached to the vendor's network unless sufficiently encrypted with even more controls guarding the public and private encryption keys. Basically, no XBOX should ever store credit card information, only account information at the very least. Even then, the credit card info that CAN be saved on Microsoft's servers can contain the CC number, cardholder name, service code and expiration date (cardholder data), but it CANNOT store the PIN, magentic stripe data or CAV2 code (card authentication data).